The Amazon search actions I found all opened up the Amazon website in a Safari window. I wanted mine to open the Amazon app itself. This URL action does that using an app-specific non-HTTP URL: https://actions.getdrafts.com/a/1GM
There’s a list of iOS app URL schemes here I haven’t tried others yet.
I’m sure this is not news to many but as a new Drafts user with very limited awareness of iOS mechanics I find this super useful.